One cutting accessory used to perform a surgical procedure is the bur. A bur generally consists of a head formed from rigid material, typically metal, shaped to have a number of flutes. The flutes are formed to define cutting edges. More particularly, the flutes are typically designed to cut hard tissue, such as bone or cartilage. A shaft extends rearwardly from the head. The proximal end of the shaft often has a feature that facilitates locking the shaft to a powered handpiece. The actuation of the handpiece results in the rotation of the bur. During a surgical procedure, the bur head is placed against a surgical site where a section of tissue is to be removed. The rotating cutting edges excise tissue away from the surgical site. Burs of various shapes and sizes are used in procedures such as orthopedic surgery, neuro and spinal surgery, ear noise and throat surgery and in other surgical procedures in which a sub-procedure is to selectively remove a section of tissue.
Burs work well for the purposes for which they are designed. Nevertheless, a problem associated with some burs is chatter. Chatter is the back and forth vibration of a bur head against the surface to which the bur head is applied. Chatter occurs as a result of bur's individual cutting edges repeatedly being forced against the tissue against which the bur head is applied.
In order to minimize chatter, burs have been proposed with different shaped as well as burs with different spacing between the flutes. The Inventors' Assignee's US Pat. Pubs. No. 2009/0048602 published 19 Feb. 2009, No. US 2012/0150209 published 13 Jun. 2012 and No. US 2012/0158028 published 21 Jun. 2012 disclose burs having flutes shaped and arranged to minimize bur vibration. Each of these publications is understood to be incorporated into reference into this application.
The above burs do have features that in some situations do serve to minimize bur vibration. Still there are some applications in which many burs when applied to soft or hard tissue, may still appreciably vibrate.
Also, there may be some procedures in which the surgeon using the bur may want to apply the bur in a backwards manner against the tissue the bur is being employed to remove. Here “backwards” is understood to mean that instead of applying a force that moves the bur away from the practitioner or sideways, laterally relative to the longitudinal axis of the bur, the surgeon draws the bur back towards himself/herself. This type of manipulation is employed if the tissue to be removed is difficult to remove by the mere pressing of the bur in the forward direction or sideways. A problem using some burs to perform this type of procedure is that their flutes do not extend a significant distance proximally behind their equators, the plane of bur maximum diameter. Many known burs, for example, have flutes that, proximally from the equator, terminate at a circle that has a diameter approximately equal to one-half of the diameter of the bur itself. This means that proximal to this circle, the bur is fluteless. Consequently, the pressing of this proximal portion of the bur head against tissue does not serve to remove any of the tissue to which this section of the bur is applied.
Thus, sometimes in order to backwards move the fluted proximal portion of the bur head against the tissue to be removed, the surgeon invariably has to press the fluteless section of the bur head against tissue that does need removal. The rubbing of this fluteless section of the bur head against the tissue frictionally heats this tissue. There may be situations in which this frictional heating results in the thermal necrosis of tissue that ideally should not be affected by the procedure for which the bur is employed.
There have been efforts to provide burs with flutes that extend proximally back closer to the shaft from which the bur head extends. This has resulted in burs that, in a single rotation, remove more tissue than the surgeon wants to remove. This type of bur is sometimes referred to as an overly aggressive bur. Further these burs have a tendency to vibrate to the extent that the vibrations adversely affect the ability of the surgeon to control, to position, these burs.